A comprehensive analysis of recovered COVID-19 patients and dynamic trend in antibodies over 3 months using ELISA and CLIA methods.

BackgroundSince the Coronavirus disease-2019 outbreak, most studies have focused on etiopathogenic aspects and treatment strategies. Acquired immunity still remains a dilemma. The aim of our study included a comprehensive analysis of patient characteristics, evaluation of antibody response, and its trend over a period of three months in recovered patients. MethodsMonocentric investigator-initiated pilot longitudinal observational study conducted by the Association Naso Sano, on a cohort of 30 COVID recovered patients based in the Umbria region, followed up from April to June 2020 for baseline blood counts, IgM and IgG trends using two different serological assays-ELISA and CLIA. The demographics, blood group, co-morbidities and treatment modalities were recorded from each patient along with an analysis of clinical profile, dates concerning symptom onset, first positive and two consecutive negative swabs using an online questionnaire followed by serological testing. Descriptive and Bivariate (Pearson correlation coefficient) statistics were conducted to detect statistically significant correlations. FindingsThe study involved 30 patients with a M:F ratio of 0.57 and a distribution of mild (67%), moderate (30%) and critical (3%). Majority of the patients were healthcare workers (40%) and the mean viral shedding duration was 20.13 {+/-} 6.17 days. The IgG levels offered long-standing protection as long as 3 months in some cases. A statistically significant, directly proportional correlation (Pearson) exists between ELISA and CLIA values for IgM. Some patients also expressed titers lower than the detection threshold and therefore a positive RT-PCR test does not necessarily guarantee a high IgG response in the recovery period. InterpretationThe data presented in our study provides a relative long-term analysis and possible explanation regarding the protection developed by patients recovered from COVID-19.